Question

A hydrated chloride of metal contains 18.26% metal and
32.42% chloride ion by mass. The specific heat of metal is
0.16. What is hydrated chloride?​

Answer 1

Given:

• The % of metal = 18.26%
• The % of chloride = 32.42%
• Specific heat of metal (c) = 0.16

To find:

The formula of the hydrated chloride.

Solution:

• According to Dulong-Petit's law, the product of atomic mass of the metal and the specific heat is equal to 6.4
• If molar mass of metal is M, M*c = 6.4 ⇒ M = 6.4/0.16 = 40 g/mol. The metal is calcium.
• Let the molar mass of the hydrated chloride be Mm.
• 18.26*Mm/100 = 40 ⇒ Mm = 219 g/mol
• Mass of chloride ions = 32.42*Mm/100 = 71 g
• One mole chloride ion weighs 35.5 g, so each mole of the hydrated chloride contains two mole of chloride ions
• Mass of water = 219-71-40 = 108 g
• Moles of water present in one mole of the salt = 108/18 = 6
• Hence the metal chloride is CaCl₂.6H₂O

Answer:

The formula of the hydrated chloride is CaCl₂.6H₂O